This invention relates to a focal length adjusting assembly for binoculars which adjusts and holds a central focusing rod in a click-stop position for automatically holding the eye pieces in a position for viewing an object at an infinite distance up to now, apparatus in which the ocular adjusting mechanism is moved by rotation of a manipulating lever or by adjusting of a dial-like manipulating lever have been used as visual regulators. However, in those apparatus the distance adjusting mechanism cannot be held at a position for viewing an object at an infinite distance because the manipulating lever and adjusting dial can be freely rotated.
Accordingly, the focal lengths in the prior art adjusting devices have been easily changeable and could not be held at the position for viewing an object at an infinite distance. Therefore, the focal lengths had to be frequently adjusted for use. Furthermore, the prior art adjusting devices could not be adjusted to and held at the position for viewing an object at an infinite data.